1. Field of the Invention
The present invention generally relates to a patient interface assembly for use in a pressure support system, and, in particular, to a patient interface assembly that is supported under at least a portion of the patient's mandible, and to a gas delivery system that incorporates such a patient interface assembly.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle or an auto-titrating pressure that varies with the monitored condition of the patient. Typical pressure support therapies are provided to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), or congestive heart failure.
Non-invasive ventilation and pressure support therapies involve the placement of a patient interface device, which is typically a nasal or nasal/oral mask having a rigid frame supporting a mask cushion, on the face of a patient to interface the ventilator or pressure support device with the airway of the patient so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such masks on the face of a patient by a headgear situated on top of the patient's head having upper and lower straps, each having opposite ends threaded through connecting elements provided on the opposite sides and top of a mask.
Because such masks are typically worn for an extended period of time, it is important the headgear maintain the mask in a tight enough seal against a patient's face without discomfort. For example, in providing CPAP to treat OSA, the patient normally wears the patient interface device all night long while he or she sleeps. One concern in such a situation is that the patient interface device be supported on the user in a stable fashion so that the mask does not shift on the patient as he or she moves during sleep. Another concern is that the user does not perceive the mask to be suffocating, i.e., minimize any claustrophobic effects the user may perceive. If these concerns are not addressed, the patient may avoid wearing the interface device, defeating the purpose of the prescribed pressure support therapy. It is also important that the interface device provide a tight enough seal against a patient's face without discomfort.
U.S. Pat. No. 2,241,535 shows an apparatus for delivering breathing gas to a patient including a nose piece having two tubes extending from lower corners of the nose piece on either side of the patient's mouth and joining together in a transverse tubular member directly resting on the anterior portion of the patient's chin. The transverse tubular member rests on or above the anterior portion of the mandible. The term “mental protuberance” is used to describe the protrusion of the anterior portion of the mandible that constitutes the chin. While this term refers to a part of a bone, it is used herein to define the entire structure of bone and overlaying skin. Thus, the device taught by the '535 patent rests just above the mental protuberance.
While the mask assembly shown in the '535 patent addresses some of the above concerns, for example, by avoiding placing portions of the interface near the patient's eyes, it does not provide a stable platform that supports the nose piece. Thus, a need still exists for a mask that more completely addresses these concerns.